Next week's Thanksgiving Holiday and the related feasts will start the familiar (awkward) two-step of "personal conduct" resolutions. After the gorging is over - and the pangs of guilt set in - many will again point toward New Year's Eve as the starting point for (now serious) plans to lose weight. This time around, one of the aspects of "watching one's weight (gains)" will be much easier. As reported in this column before, small-scale studies have presented some evidence that posting calories for menu items leads to slight changes of behavior. Starting in January, according to the recently passed health care law, this kind of experiment will be run on a large scale, namely nationwide. The majority of restaurant chains must then inform their patrons in detail about calorie counts. Right on time, a new study about weight and fitness has just been posted as a working paper (that description means that it has not yet completed the rigorous scientific screening necessary for publication). Its message may be surprising to some. In the study titled "Is poor fitness contagious? Evidence from randomly assigned friends," the authors attempt to identify whether there are any effects of friends' behavior(s) with respect to one's own fitness. The three authors are at it again, analyzing a unique data set regarding students at the U.S. Air Force Academy. (Regular readers of this column may remember another study in which they utilized this data to analyze student drinking behavior.) Scott Carrell (UC Davis), Mark Hoekstra (Pittsburgh) and James West (U.S. Air Force Academy) take advantage of the fact that freshmen at the academy are randomly "assigned to squadrons of approximately 30 students with whom they are required to spend the majority of their time." Random assignments are the gold standard of scientific analysis because they are often necessary to be able to draw strong causal conclusions without having to account for all kinds of statistical biases. The authors possess data on 3,487 freshmen, which does not just include their physical fitness results at the academy but - most importantly - high-school fitness measures from long before they became friends with randomly assigned academy buddies. Of course, as is pointed out repeatedly in this manuscript, by definition recruits at the academy are likely to be fitter than the average member of the U.S. population. Nevertheless, even after taking this into account, the authors are able to deduce a strong causal effect of friendship on fitness. Not only can they present overwhelming evidence that the type of friend one keeps (even randomly assigned) matters with regard to fitness levels. The authors can even parse out whether the observed correlations are due to fitness buffs lifting up their peers or to slackers dragging others down. As it turns out, the latter is the case. At one point in the paper, it states: Our results "indicate that the peer effects in physical fitness ... are primarily driven by the least physically fit friends. Second, the individuals most at risk from exposure to unfit friends are those who themselves struggle with fitness." Thus, there may be one more Thanksgiving/New Year's resolution in order: Pledge to include your least physically fit friends in your ramped-up sports activities. Otherwise, they will just drag you down and Thanksgiving 2011 will see you considering exactly the same resolution again.

Dr. Michael Reksulak teaches economics and public finance in Georgia Southern University's College of Business Administration. He may be reached by e-mail at mreksula@georgiasouthern.edu.